A well-known storage format meeting this definition has been standardized under the name of Universal Disk Format UDF and published in OSTA Universal Disk Format Specification, by Optical Storage Technology Association, 311 East Carrillo Street, Santa Barbara, Calif. 93101, USA, Copyrighted 1994-1997. UDF is platform-independent and has an advantageous degree of flexibility. As requested by the UDF, each descriptor will be stored in a separate logical sector. Various instances discussing the descriptor format and usage have been given on pages 7, 8, 17, 19, 20-25, 34-38, 44-49, 50, 57, of the above document. Now in particular, according to the standard, the size of the logical sector is uniform for storing data blocks as well as for storing descriptors. The environment of the present invention is directed to physically exchangeable storage items.
Now, for so-called streaming storage devices, and also for devices-with a large storage capacity such as surpassing 10 Gigabytes and used for digital tape drives and other, it is necessary to employ large physical sectors that may have a capacity such as 32 kBytes, and represent the smallest separately addressable storage items. However, most descriptors have a size only in the range between 0.25 and 1 kBytes. Evidently, this would result in throwing away a large part of the available storage space, with each descriptor requiring its own physical sector. Moreover, the reading of directory information would require an exceptionally long time, especially in the case of streaming devices, in particular, because the reading of a 1 kB descriptor would take the same time as reading a 32 kB physical sector. The problem is aggravated where drive apparatuses for newer, high capacity, storage media will take relatively much time for operations such as in particular tape winding, rewinding, and head positioning. In this context, an additional trend is directed towards using larger physical sectors, which aggravates the problem.
In consequence, amongst other things, it is an object of the present invention to formulate a storage procedure that would allow the use of larger physical sectors whilst keeping directory access time at a low value, and also to maintain storage efficiency through allowing the filling of directory sectors and certain other sectors, such as those used for storing metadata.
Now therefore, according to one of its aspects the invention is characterized by assigning descriptor items to a dedicated and immediately accessible directory space, and within the directory space, mapping successive logical sectors at mutual stepping distances that are a factor less than a physical sector size which size is uniform among data and descriptor items. The descriptors may contain volume and directory information, and file attributes, also known as metadata.
The invention also relates to a large-capacity and/or streaming storage device for implementing the invention and a storage medium driver arranged for accessing such medium. Further advantageous aspects of the invention are recited in dependent Claims.